Geography 2220A/B Lecture Notes - Lecture 3: Geographic Coordinate System, Gnomonic Projection, Grs 80
21 Jan 2020
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Geographic info that has been encoded as spatial data= has geographical/ spatial referents attached (uniform; not uniformed) n i. e. longitude & latitude; street address; postal code. Defined how the ellipsoid is "fixed: defines the origin & orientation of longitude + latitude, earth"s mass center. Gcs named referred by datums (nad27-clarke 1866; nad83-grs80;wgs84-refined version of grs80; slightly more accurate; baseline for gnss, e. g. gps) w conversion know as a datum transformation n translates coordinates from one gcs to another. Map projections 3d 2d: projected coordinate system (pcs) always based on a gcs -> ellipsoid. Unlike gcs, pcs has constant lengths (d), angles, shape (peel an organge) 2 "cases": w w tangent "flush" w/ the globe. Standard parallel, (1/2~) w distortion least (most accurate projection) Orientation of the developable surface as it "contacts" the ref globe. Gnomonic projection w light source is center of the ref globe w w can only project half of the globe great circles projected as straight lines.
